A diagnosis apparatus as a tool for diagnosing a trouble occurred in a vehicle is known in the prior art. But, knowing a cause of a trouble by reproducing the trouble or failure is helpful to repair the trouble. When a trouble of a vehicle introduced into an automobile repair shop cannot be reproduced, it is difficult to diagnose. Reproducing the trouble through trial and error by changing operating conditions such as vehicle speed and engine water temperature may be performed, but it requires a tremendous effort.
Patent literature 1 described that, with the use of driving data produced and stored in an electronic control unit when a trouble took place, the vehicle is driven in a trouble reproduction mode and the driving data acquired is compared with the driving data produced when the trouble took place. Matching of driving conditions is informed to a tester.
However, as driving data includes a large number of parameters, it is difficult to bring all parameters close to the parameters when the trouble took place. Further, if diagnosis of the trouble is done with very limited parameters, validity of the diagnosis is suspicious. The electronic control unit stores an array of instantaneous values of numerical values that are unique to the specific vehicle so that a range of values appropriates for a trouble diagnosis is hard to establish. Accordingly, the range of values appropriates for reproduction of a trouble is hard to establish.
From time to time, a diagnosis apparatus cannot determine what parameters are important for reproducing the trouble, thus, diagnosis has to rely on the skill of the engineers who perform diagnosis.
On the other hand, sometimes repair manual provides conditions for performing diagnosis in accordance with trouble codes. As the conditions are set according to general designing criteria, the range of numerical values is too large to focus, making diagnosis difficult.